2D Materials for Large-Area Flexible Thermoelectric Devices

The rapid development of the concept of the Internet of Things (IoT) requires wearable devices with maintenance-free batteries, and thermoelectric energy conversion based on large-area flexible materials has attracted much attention. Among large-area flexible materials, 2D materials, such as graphene and related materials, are promising for thermoelectric applications due to their excellent transport properties and large power factors. In this Review, both single-crystalline and polycrystalline 2D materials are surveyed using the experimental reports on thermoelectric devices of graphene, black phosphorus, transition metal dichalcogenides, and other 2D materials. In particular, their carrier-density dependent thermoelectric properties and power factors maximized by Fermi level tuning techniques are focused. The comparison of the relevant performances between 2D materials and commonly used thermoelectric materials reveals the significantly enhanced power factors in 2D materials. Moreover, the current progress in thermoelectric module applications using large-area 2D material thin films is summarized, which consequently offers great potential for the use of 2D materials in large-area flexible thermoelectric device applications. Finally, important remaining issues and future perspectives, such as preparation methods, thermal transports, device designs, and promising effects in 2D materials, are discussed.